1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
In recent years, digital printers employing an electrophotographic process have been increasingly used in the field of production printing. Therefore, there is a demand to improve image quality and reliability in the digital printers employing the electrophotographic process. In particular, in the digital printers employing the electrophotographic process, there is a demand to improve the reproducibility of thin lines, improve the reproducibility of characters (improve the reproducibility of characters with minute sizes corresponding to two or three points, for example), prevent thickening of the characters due to the electrophotographic process, and improve the accuracy for color shift.
To improve the image quality, a digital printer employing the electrophotographic processes includes an image processing unit that corrects image data through image processing. The image processing unit performs image processing by using multi-bit data with a high resolution of 1200 dots per inch (dpi) or 2400 dpi, for example.
The digital printer employing the electrophotographic process includes a photoconductor drum with a surface serving as a scanning surface having photosensitivity, a light source that emits a laser beam, a polygon mirror that deflects the laser beam from the light source, and a scanning optical system that guides the laser beam deflected by the polygon mirror to the surface (scanning surface) of the photoconductor drum. The digital printer employing the electrophotographic process modulates a light flux emitted from the light source in accordance with image data, irradiates the scanning surface with the light flux from the light source, and scans the scanning surface with the light flux, thereby forming an electrostatic latent image corresponding to the image data on the photoconductor drum.
The digital printer employing the electrophotographic process configured as described above uses an element with a plurality of light-emitting points, such as a laser diode array (LDA) or a vertical-cavity surface-emitting laser (VCSEL), as the light source. Therefore, the digital printer employing the electrophotographic process can form an electrostatic latent image with a resolution of, for example, 2400 dpi or 4800 dpi, which is higher than that of image data with the resolution of 1200 dpi.
Japanese Patent No. 4968902 and Japanese Patent No. 4640257 disclose a technology for detecting an outline portion in an image and enhancing an outline line or correcting pixels around an outline character through a process by the image processing unit to thereby prevent reversed characters from becoming broken and improve the reproducibility of the characters. Japanese Laid-open Patent Publication No. 2008-85487 discloses a technology for causing a controller to thin a line and perform smoothing simultaneously by using template matching with multi-value data.
Incidentally, if image processing is performed with a high density, a defect may occur in data transfer from the image processing unit to a light source driving circuit on the downstream side. If multi-bit data with a resolution of, for example, 2400 dpi or 4800 dpi, is used by the image processing unit, the flexibility of image processing is increased and the reproducibility of minute characters or lines of 1200 dpi can be improved. However, if the image processing is performed with a high density, the amount of data transferred from the image processing unit to the light source driving circuit on the downstream side greatly increases, which is the bottleneck of the productivity.
If all of the processes for improving the reproducibility of minute characters or the like are performed by the image processing unit on the upstream side, the processes become complex and loads on the image processing unit increase.
In view of the above circumstances, there is a need to improve image quality by performing image processing with a high resolution without increasing the amount of image data to be transferred.